The invention relates to a lifting device for raising, lowering and moving a load. The lifting device has a drive wheel, a friction disk brake, a load wheel and a gear, which are arranged sequentially in an axial direction inside a housing. The drive wheel can be coupled with the gear by way of a drive shaft which extends through the friction disk brake and the load wheel. The gear is located on the drive shaft on the opposite end from the drive wheel and transfers torque to the load wheel.
Lifting devices of this type are used particularly for loads that are to be moved vertically. Such lifting devices include a drive wheel, which is frequently implemented as a chain wheel and can be rotate in both directions using a manually operated round link chain. However, instead of the chain wheel, a toothed wheel can also be used. Moreover, the drive wheel can be implemented as a coupling wheel for coupling to a motor shaft.
The load wheel which is typically implemented as a chain wheel, is coupled through a round link chain with a load receiving means, for example a crane hook.
The housing of the lifting device is typically provided with a hook for suspending the housing from suitable support bearings.
The drive wheel, a friction disk brake, the load wheel and a gear are arranged sequentially in an axial direction inside the housing, with the gear frequently having the form of a planetary gear. The drive wheel sits on one end of a drive shaft which extends through the friction disk brake and the load wheel. The gear is located on the other end of the drive shaft which is connected to the load wheel in order to transmit torque.
In a known design of a lifting device of the aforedescribed type (brochure from Yale industrial products GmbH, 5620 Velbert 1 xe2x80x9cYale Flaschenzug/Hoist/Palan à bras Mod. VSxe2x80x9d), the friction disk brake is comprised of a ratchet disk, of friction disks disposed on both sides of the ratchet disk, as well as of two detents which are pivotally supported on the housing and urged by leg springs against the ratchet disk. The two friction disks are frictionally coupled, on one hand, with the ratchet disk and, on the other hand, with a pressure disk affixed to the shaft or the drive wheel, respectively. The drive wheel is axially moveable on a thread disposed on one end of the drive shaft. The other end of the drive shaft is coupled with two toothed wheels which are operatively connected with a toothed wheel by toothed pinions having a smaller diameter. The toothed wheel has inside teeth in which a pinion engages which in turn is coupled with the load wheel.
The friction disk brake is provided to hold the load carried by the lifting device at a respective height when the drive wheel is stopped. In this case, the drive wheel is pressed via the friction disks and the ratchet disk against the pressure disk. The detents rest in the peripheral recesses disposed on the ratchet disk.
When the drive wheel is rotated in the direction for raising the load, the detents slide across the teeth of the ratchet disk until the drive wheel stops. The detents then engage again with the recesses of the ratchet disk. When the load is lowered, the drive wheel rotates in the opposite direction, thereby axially sliding on the motion thread of the drive shaft, so that the frictional contact with the friction disks, the ratchet disk and the pressure disk is eliminated. The load can then descend until the coasting shaft once more compensates the axial play.
It would be desirable to improve the conventional design because the friction disk brake can fail when foreign particles enter the brake or the coil springs break. In addition, the noise originating from the detents are objectionable in many applications, in particular where this noise produces a noxious noise level. Moreover, the friction disk brake, in particular the ratchet disk, is expensive to manufacture.
It is therefore an object of the invention to provide a lifting device of a simpler design, which is less susceptive to malfunction and produces less noise.
According to one aspect of the invention, the drive wheel can rotate relative to the drive shaft within certain limits, but is prevented from moving on the drive shaft in an axial direction. In addition, the drive wheel is coupled to a brake disk for limited relative rotation thereto. The brake disk can move in the axial direction on a threaded section of the drive shaft. A friction disk is located between the brake disk, and a pressure disk is attached to the housing of the lifting device.
When the load is to be raised, the drive wheel is rotated clockwise. After a predetermined rotation angle over which the drive wheel can rotate freely relative to the drive shaft, the free rotation ends and the drive shaft is driven directly by the hand wheel, without loading the brake. Since the threaded sections have a right-handed thread, the brake disk is released from the friction disk for clockwise rotation, thereby canceling the braking action.
When the rotation of the drive wheel is stopped, the drive shaft which rotates under the influence of the load, pulls the brake disk against the friction disk and thereby against the pressure disk. The load is arrested.
For lowering the load, the drive wheel has to be turned counterclockwise. After a predetermined rotation angle, the drive wheel is coupled with the brake disk. The brake disk is axially displaced on the threaded section towards the drive wheel due to the right-handed thread section, so that brake disk does no longer contact the pressure disk via the friction disk. The load can then coast according to the predetermined rotation angle between the drive wheel and the brake disk. The load is braked in that the drive shaft, which rotates under the load, pulls the brake disk against the friction disk and the friction disk against the pressure disk. Advantageously, the design of the invention is significantly more accurate than conventional designs and operates more quietly. The lifting device according to the invention is also less complex due to the reduced number of components.
It should also be emphasized that the drive shaft and accordingly also the load wheel are driven directly by the drive wheel, without loading the friction disk brake.
The drive wheel can be driven using a chain, a rope, a crank or a motor, as is known in the art.
According to an advantageous embodiment, the drive wheel is rotatably supported on a bushing which is secured on the drive shaft The bushing can be pressed onto the drive shaft.
According to another advantageous embodiment, for transmitting torque, one end face of the drive wheel has a projection, which cooperates with a wing disk that is non-rotatably connected with the drive shaft. After the drive wheel has rotated by a predetermined rotation angle, the projection contacts a limit stop disposed on the drive wheel and locks both the wing disk and the drive shaft to prevent relative rotation therebetween.
The position of the bushing on the drive shaft is fixed by the wing disk that is pushed onto the drive shaft and prevented from rotating relative to the drive shaft.
The wing disk is preferably pushed onto a serration located on the end of the drive shaft and pressed against the bushing by a nut, with a radial collar of the bushing being pressed against a shoulder of the drive shaft. The drive wheel is thereby precisely guided between the radial collar and the end face of the wing disk facing the radial collar. The wing disk includes at least one radially projecting wing which cooperates with at least one projection provided on the end face of the drive wheel. The free rotation of the drive wheel on the drive shaft is limited by the cooperating projection and wing. The load can then be raised by the drive wheel. Preferably, the wing disk has two radial wings that are mutually offset by 180xc2x0. Two corresponding projections, which cooperate with the wings are then also provided on the end face of the drive wheel; in particular, the projections cast as one piece with the drive wheel.
According to yet another advantageous embodiment, the brake disk has a driven pin which is oriented in the axial direction and has a radial spacing to the drive shaft. The driven pin can move relative to and engage with a segmented recess of the drive wheel located on a side facing the load wheel. The driven pin catches the segmented, preferably arcuate, recess. The ends of the recess in which the driven pin engages, are formed by radially oriented ribs. The brake disk is entrained by the drive wheel in order to lift the brake disk from the pressure disk when the load is lowered, so that the friction disk brake is released.
According to still another advantageous embodiment, the brake disk is pressed against the pressure disk by a spring supported on the drive wheel. This spring is intended to produce an initial braking torque, thereby reducing the response time of the friction disk brake.
Further features and advantages of the present invention will be apparent from the following description of preferred embodiments and from the claims.